In situ growth of ZIF-67 to construct core–shell mosaic structural composites for efficient extraction of benzoylurea insecticides

A novel mosaic structure Silica@C/Co@ZIF-67 composite was synthesized by successfully embedding Co nanoparticles on the surface of silica spheres with the help of thermoplastic polyethyleneimine by carbon-reduction. The ZIF-67 half-shell layer structure was synthesized by the in-situ growth of ZIF-67 on the surface of silica spheres through the coordination of 2-methylimidazole with Co metal nodes. The composite was used as a magnetic solid-phase extraction adsorbent combined with high performance liquid chromatography-ultraviolet detector (HPLC–UV) for the extraction and determination of benzoylurea insecticides (BUs) in vegetables and tea. Based on the presence of π-π, hydrophobic and hydrogen bonding interactions between Silica@C/Co@ZIF-67 and BUs, the BUs were rapidly captured by the composites resulting in high adsorption performance. Under the optimal extraction parameters, the linear ranges were 0.3–200 µg L⁻¹ for diflubenzuron, 0.6–200 µg L⁻¹ for chlorbenzuron, and 1.0–200 µg L⁻¹ for triflumuron, teflubenzuron, and flufenoxuron, with correlation coefficients (R²) greater than 0.9991. The limits of detection (LODs) of the method were 0.1–0.3 μg L⁻¹, and the relative standard deviations (RSDs) were 1.2–3.0% for intra-day and 2.6–4.6% for inter-day. In the spiked recovery experiments of vegetables and tea, the recoveries of the five kinds of BUs ranged from 75.8 to 112.9%. In addition, after 10 repetitions using Silica@C/Co@ZIF-67, the recoveries of the five kinds of BUs were still as high as 78.4 to 83.9%.